Many people suffering from vestibular disorders often complain of balance problems and loss of spatial orientation. Yet, our knowledge regarding sensory (perceptual) recovery after vestibular damage remains limited and all we currently know about vestibular compensation has been based primarily on VOR deficits. Furthermore, neurophysiology experiments characterizing vestibular compensation have made no attempt to measure interneuronal correlations or correlations between neural activity and behavior (e.g., choice probabilities CP); both of which affect population decoding for sensory perception. There are three goals in the present experiments. First, we will compare neuronal thresholds in the vestibular (VN) and cerebellar (CN) nuclei, as well as parietoinsular vestibular cortex (PIVC) simultaneously as trained animals perform rotation discrimination tasks to test contemporary theories of sensory encoding and decoding. Second, we will characterize deficits and compensation in vestibular rotation perception after unilateral labyrinthectomy (UL). Results will not only be informative for vestibular rehabilitation and recovery of function, but will also provie vital tests of computational theories of sensory perception. Third, we will investigate whether noise in semicircular canal afferents contributes to perception. While macaques perform a direction discrimination task, we will search for trial-to-trial correlations between canal afferen activity and perception. Such correlations, often found in cortical neurons, are thought to reflect top-down influences. The present experiments seek to provide evidence for or against an opposite, bottom-up, hypothesis, i.e., that sensory noise propagates through to the decision. The proposed experiments represent a paradigm-shift for studying neural processing in the vestibular system. The outcomes of the proposed studies will not only be very useful for understanding perceptual deficits and recovery of spatial orientation, but will also contribute valuable and important knowledge about sensory processing and neuronal variability more generally.